Canadian Patent Application Serial No. 439,146, filed on Oct. 17, 1983 by the present applicant, describes a novel method and apparatus for monitoring the health and/or degree of wear of machinery. The primary objective of such apparatus is to maximze human safety by forestalling failure and minimize downtime and its associated expense and inconvenience.
In essence, the described method is based on the premises that (a) wear debris concentration and particle size increase as the rate of wear increases, (b) the frequency of the output signal of an oscillator is directly related to the permeability of the inductance coil of the oscillator, and (c) the permeability is related to the mass of ferromagnetic material in the core of the coil. The method involves passing a stream of a fluid containing ferromagnetic particulate material, the concentration of which is to be determined, through a flow tube having an electromagnetic trap disposed about the flow tube upstream of a sensing ciol also disposed about the flow tube. The sensing coil forms part of an oscillator circuit which, in turn, forms part of a larger electrical circuit which monitors and processes the output of the oscillator. At predetermined time intervals, the electromagnet is energized for a period of time to trap ferromagnetic particulate material on the inside of the flow tube. De-energization of the electromagnet releases the trapped material into the fluid stream toward the sensing coil. Flow of the accumulation passed the sensing coil causes a slight reduction in the frequency of the signal of the oscillator and the magnitude of the change of the frequency together with the elapsed time within which the fluid passes through the sensing coil are employed to determine the concentration of the ferromagnetic particulate material in the fluid. Thus, the change in frequency is determined as a transient signal following the trapping event.
While the method and apparatus operate quite successfully, the process for determining the concentration is somewhat complex and the detector is relatively bulky.